Method for the continuous casting of tubes

ABSTRACT

Apparatus for the continuous casting of tubes includes a mandrel which extends into the mold. The diameter of the mandrel is expandable and contractable, suitably by having the mandrel composed of radially movable segments. During casting the diameter of the mandrel is expanded when there is no relative movement between the tube being formed and the mandrel, and is contracted when the tube moves relatively off the mandrel. In oscillating molds, in which the mandrel also oscillates, there would be no relative movement between the mandrel and the tube during the downward movement of the mandrel, during which the mandrel is expanded. On the upward movement the mandrel would be contracted.

tlnied tates Patet Simone Feb. 1, 1972 [54] METHOD FOR THE CONTINUOUS 1,747,679 2/1930 Perry ..249/l80 X CASTHNG 0F TUBES 2,405,254 8/1946 Hopkins ..249/82 X 2,676,372 4 1954 Venner eta]. ..249 180 [721 Invent: Sim, Duesseldmfl Germany 2,740,177 41956 Smart Jr. 16 4/85 [73] Assignee: Schloemann Aktiengesellscheft, Duesseldorf, Germa y Primary Examiner-R. Spencer Annear A t d C l' Filed: Feb- 1970 tarney San 0e Hopgooddz aimafde [21] Appl. No.: 14,298 ABSTRACT Apparatus for the continuous casting of tubes includes a man- [30] Foreign Application Prigrity D m drel which extends into the mold. The diameter of the mandrel is expandable and contractable, suitably by having the man- Feb. 27, 1969 Germany drel composed of radially movable Segments. During casting the diameter of the mandrel is expanded when there is no relagi ts}? five movement between the tube being formed and the drel, and is contracted when the tube moves relatively off the [58] FieldofSem-ch ..l64/83,85,260,273,280,' d l I Id h h d l l 164/281 249/82 18o man re. noscuamgmo s, mw1c t eman re asooscilates. there would be no relative movement between the man- 0 drel and the tube during the downward movement of the man- [56] Referenfij Cited drel, during which the mandrel is expanded. On the upward UNITED STATES PATENTS movement the mandrel would be contracted.

858,480 7/1907 Sprague ..249/ 180 X 3 Claims, 5 Drawing Figures rp /O l l m 1, a a "-20 I j 5/ I I N l0 4 9 a e V /8 /l METHOD FOR THE CONTINUOUS CASTING OF TUBES The present invention relates to a method and apparatus for the continuous casting of tubes in a continuous casting mold into which a mandrel extends. It is known in the art to circulate coolant in mandrels in order to obtain solidified skins of the same thickness on both the outside and the inside of the tubes. It is also known to give the mandrel a conical shape in order to decrease the possibility of the tube shrinking on the mandrel.

The shrinkage gap between the mold wall and the outside of the tube increases during the cooling of the casting. This results in a decrease of the heat transfer between the mold wall and the outside of the tube, which in turn decreases the cooling rate of the strand. This stable condition between shrinkage and heat transfer does not apply to the relationship between the mandrel and the inside of the tube, because here the shrinkage causes an increase in the heat transfer, which in turn increases the shrinkage and so on. This process accelerates itself and results in a shrinking of the tube on the mandrel. It can only be prevents by using a mandrel which is so extremely conical, that the tube could not shrink on it, despite the above described mutually accelerating relationship between shrinkage and heat transfer. However, the provision of such a large shrinkage gap would greatly reduce the heat transfer and therefore the casting speed.

A principal object of the present invention is a method and apparatus for the continuous casting of tubes in a continuous casting mold into which a mandrel extends which prevents the tube from shrinking on it, while the shrinkage gap is kept at a minimum, thereby insuring good cooling of the tube. According to the invention this is accomplished by decreasing the diameter of the mandrel before the start of a relative movement between the tube and the mandrel and then to increase again the diameter of the mandrel to this original size after said relative movement is completed.

In a further development of this invention for use in casting machines with intermittent strand withdrawal, the diameter of the mandrel is decreased before the beginning of the withdrawal and is increased again to its original size after the end of the withdrawal.

The invention can also be used in casting machines with continuous strand withdrawal by using an oscillating mandrel. The diameter of the mandrel is decreased before the beginning of the return stroke and is increased again to its original size before beginning its forward stroke which has the same direction as the strand movement.

In this way the sliding of the tube on the mandrel is considerably facilitated; A shrinking of the tube on the expanded mandrel ends when the diameter of the mandrel is decreased before the beginning of the relative movement between mandrel and tube, preventing interruptions in the strand withdrawal and ruptures of the solidified strand skin.

An apparatus for performing the above described method comprises according to the present invention an inner guide device of a mandrel, which guides a lift tube which is adjustably actuated by a power cylinder and is concentrically surrounded by mandrel segments which are held together by springs. The lift tube has inclined surfaces which are matched by correspondingly inclined surfaces of the mandrel segments. All inclines surfaces are inclined in the direction of the lift tube movement. The lift tube may be screwed into the ring piston of a double acting power cylinder which is attached to the mandrel support.

In an alternative design the lift tube can be replaced by a tube having surfaces with intermittingly increasing and decreasing radii, so that a turn of the tube moves the mandrel segments radially outwards, thereby expanding the mandrel.

it is advantageous to provide guide rolls at the lower part of the guide device when all of the mandrel surface consists of movable segments.

in still another design radially movable segments are located between and protrude beyond fixed segments, which are attached to the guide device. The corrugated solidified skin of the casting is therefore able to contract when the movable segments are pulled back, thereby eliminating the danger of the tube shrinking on the mandrel. The outside diameter of the mandrel segments may decrease in the direction of the strand travel, as is known in the prior art. The segments have cooling channels which are supplied by flexible hoses.

The inside of the tube is cooled by spray nozzles which are located at the lower part of the guide device and which are supplied with cooling water through a central duct in said guide device.

Illustrative embodiments of the invention are shown in the accompanying drawings in which:

FIG. 1 is a vertical longitudinal section through a mandrel of this invention protruding into a mold;

FIG. 2 is a cross section of a mandrel having movable segments;

FIG. 3 is a cross section of a mandrel having both fixed and movable segments;

FIG. 4 is a cross section of a mandrel having both fixed and protruding movable segments;

FIG. 5 is a vertical longitudinal section through a machine having two molds for the continuous casting of tubes.

Referring to the drawings, a mandrel support 2 with a guide device 3 attached to it is located above the inlet end of continuous casting mold l. A lift tube 4 slides with its sliding sleeves 5 and 6 on the guide device 3. The lift tube 4 is screwed into the ring piston 7 of a power cylinder 8 which is attached to the mandrel support 2. The lift tube 4 has inclined upper and lower surfaces 9 respectively 9, which are matched by correspondingly inclined surfaces 10 respectively 10 of the mandrel segments 11.

The mandrel segments 11 are arranged in a circle around the lift tube 4 and are held together by upper and lower circular springs 12 and 12'. The upper ends of the segments 11 are contained in a recess of the mandrel support 2, while the lower ends rest on a shoulder 3' of guide 3.

The mandrel support 2 has a cooling water inlet box 13 and a cooling water outlet box 14. Inlet pipes 15 and flexible hoses l6 connect the inlet box 13 with the cooling water channels 17 of the mandrel segments 11. A return passage 18 connects the channels 17 with the cooling water channels 19 of the mandrel segments 1 l. Accelerator rods 20 are placed into the channels 19 to increase the water velocity. Flexible hoses 21 and pipes 22 connect the channels 19 with the cooling water outlet box 14.

Cooling water is supplied through an inlet pipe 23 and a passage 24 in the guide 3 to spray nozzles 25 which are arranged at the lower part of guide 3 and cool the inside of the tubes. Tube guide rolls 26 are also located at the lower part of guide 3.

An alternative mandrel design is shown in FIG. 3 in which fixed segments 11a are located between radially movable segments 32. The upper and lower ends of the fixed segments llla are connected to the guide 3. In still another alternative mandrel design shown in FIG. 4 the fixed segments 27, which are located between the movable segments llb, are also connected with their upper and lower ends to the guide 3. Since the movable segments 11!; protrude beyond the fixed segments 27, a corrugated surface is created which further minimizes the possibility of the tube shrinking on the mandrel.

The method of the invention can be practiced with the above described apparatus in the following manner:

Molten metal is poured continuously into mold 1. Mold 1, mandrel support 2 and the mandrel are continuously oscillated in such a way that equal speeds are obtained between the mandrel and the tube 28 during movement in strand withdrawal direction. During this movement the piston 7 and therefore the lift tube 4 are in their upper position. The inclines surfaces 9 and 9' of the lift tube 4 are also in their upper position and have pushed the mandrel segments 11 in a radially outward direction, which has increased the mandrel diameter. The piston 7 is moved to its lower position before the beginning of the return stroke of the mandrel, so that the circular springs 12 and 12' can pull back the mandrel segments, thereby decreasing the mandrel diameter.

The mandrel is fully expanded during the pouring of metal when casting intermittently. The mandrel diameter is then decreased before the beginning of the withdrawal of the casting. A particularly advantageous arrangement for such a machine is shown in FIG. 5. Two molds 1 and 1a witH tundishes 29 and 29a are arranged side by side. Molten metal is poured from a ladle 31 into a swivel launder 30 which alternately guides the metal into the tundish 29 and 290:. Such an arrangement has the advantage that the metal can be poured continuously out of the ladle, thereby preventing freezing of the ladle stopper.

lclaim:

l. A method for the continuous casting of tubes in a continuous casting mold having a radially expansible mandrel extending into it in which, during casting withdrawal, there is intermittent relative movement between the cast tube and the mandrel, which comprises expanding the diameter of the mandrel when there is no relative movement between the mandrel and the tube, and decreasing the diameter of the mandrel when there is relative movement between the mandrel and the tube to facilitate sliding of the shrinking tube on the mandrel.

2. The method of claim 1 wherein the mold and the mandrel oscillate relative to the cast tube, moving first in the direction in which the cast tube is withdrawn from the mold, with the mandrel moving first at the same speed in the same direction as the tube, and then in the opposite direction, which comprises expanding the diameter of the mandrel when the mold and mandrel are moved in the direction in which the cast tube is withdrawn from the mold and decreasing the diameter of the mandrel when the mold and mandrel are moved in the opposite direction.

3. The method of claim 1 in which the diameter of the mandrel is decreased before the start of relative movement between the mandrel and the tube and is increased after said relative movement is completed. 

1. A method for the continuous casting of tubes in a continuous casting mold having a radially expansible mandrel extending into it in which, during casting withdrawal, there is intermittent relative movement between the cast tube and the mandrel, which comprises expanding the diameter of the mandrel when there is no relative movement between the mandrel and the tube, and decreasing the diameter of the mandrel when there is relative movement between the mandrel and the tube to facilitate sliding of the shrinking tube on the mandrel.
 2. The method of claim 1 wherein the mold and the mandrel oscillate relative to the cast tube, moving first in the direction in which the cast tube is withdrawn from the mold, with the mandrel moving first at the same speed in the same direction as the tube, and then in the opposite direction, which comprises expanding the diameter of the mandrel when the mold and mandrel are moved in the direction in which the cast tube is withdrawn from the mold and decreasing the diameter of the mandrel when the mold and mandrel are moved in the opposite direction.
 3. The method of claim 1 in which the diameter of the mandrel is decreased before the start of relative movement between the mandrel and the tube and is increased after said relative movement is completed. 